Pyridoxal-5'-phosphate as an oxygenase cofactor: Discovery of a carboxamide-forming, a-amino acid monooxygenase-decarboxylase

Enzymes that activate dioxygen typically rely on flavins or transition metals as redox cofactors. We describe the discovery of the enzyme catalyst Cap15 that converts 5'-C-glycyluridine (GlyU), an unusual β-hydroxy-α-amino acid, to the modified nucleoside uridine-5'-carboxamide. In contrast to expectations, pyridoxal-5'-phosphate (PLP) is the sole cofactor that serves as the initiating reducing agent to activate dioxygen for incorporation into GlyU prior to decarboxylation. Thus, Cap15 is now classified as an O2- and PLP-dependent monooxygenase-decarboxylase. Also in contrast to expectations, phosphate and the (5'S,6'R) isomer of GlyU -- and not (5'S,6'S)-GlyU, the established pathway intermediate -- are essential for Cap15 activity. In total, Cap15 utilizes an enzymatic strategy for oxygen incorporation during conversion of an α-amino acid to a carboxamide.